Because rigid political identities are retarded and most people are retarded. When you're defining "right wing" as hates niggers and jews and "left wing" as wants to get cuckolded by a gang of muslims everything becomes meaningless. Politics is just the new sportsball where people pick the team they think has cool aesthetics then they adopt those aesthetic positions to be apart of a cool social in group.
There's a minute amount of people in the world that actually take the time to flesh out a moral framework and analyze how each individual political policy feats into said moral framework. Most people aren't capable or don't have the time to invest that much into constructing these mental systems. It's the entire reason religion exists, inheriting moral and political frameworks is infinitely more efficient for both society and the individual.